Mobile communication systems, as examples of wireless communication system, can be effected by fading. The diversity scheme is a well-known means for reducing the deterioration of channel quality caused by this fading. The diversity scheme includes two types of techniques: the transmission diversity using more than one transmitter antennas; and the reception diversity using more than one receiver antennas.
In mobile communication systems, since there is a demand for down-sizing of mobile stations, the number of antennas provided for mobile stations is limited. Thus, the transmission diversity scheme can be employed in communications from base stations to mobile stations (down-link).
Further, recently, in mobile communication systems, since there are demands for a high-speed data rate and increase in the cell capacity, multiple antenna technology, such as the MIMO technology and the array antenna technology, can be employed.
[Patent document 1] Published Japanese Translation of a PCT Application No. 2005-528038
[Patent document 2] International Publication Pamphlet No. WO 2004/095730
[Patent document 3] Published Japanese Translation of a PCT Application No. 2005-524332
To separate signals (symbols) in a reception station with the MIMO scheme, it is difficult to perform the separation without assuring reception signals of a desired reception signal intensity such as the Signal to Noise Ratio (SNR). As technology for improving such an SNR, it is possible to employ the beam forming technology in which the wireless wave directivity is arithmetically controlled by means of performing weighting control to more than one series of transmission signal in accordance with propagation path (channel) information.
To perform the beam forming in a transmission station, it is necessary for the transmission station to recognize channel information between the transmission station and a reception station. In the case of Frequency Division Duplex (FDD), it is necessary for the reception station to measure channel information and then notify the transmission station of the measurement result through a feedback channel. In the case of Time Division Duplex (TDD), it is necessary for the transmission station to measure channel information in the direction from the reception station to the transmission station based on the signals received from the reception station.